1. Field of the Invention
This invention relates to the foundry arts, and more particularly to that area of the foundry arts related to core box assemblies and the construction thereof.
2. Description of the Prior Art
Core boxes surround a void having inner surface walls in the configuration of the outer walls of a core which is formed therein of some mold material. The formed core is placed within a mold assembly into which a liquid casting material is then poured. The casting material will ultimately solidify and provide a cast article taking the shape of the mold. Cores may be used for example when the desired end cast article has a passage therethrough. In such a case, the core is formed in the core box in the shape of the passage and is laid within the mold so that when the liquid casting material (such as molten metal) is poured into the mold, that volume within the mold occupied by the core is maintained free of metal and the passage therefore appears in the end cast article. An example of such a core may be seen in copending U.S. patent application Ser. No. 238,905, filed Feb. 27, 1981. Cores are therefore generally used as part of a mold assembly to fill volumes within the mold cavity so that the ultimate shape of the cast article is attained.
Such cores for metal casting molds are generally made of a mold sand and bonding agent mixture which is poured into a core box having walls defining the core shape as noted hereinbefore. The core box sometimes defines only one portion, such as one side, of the total shape, there being a matching core box to define the opposite side of the core shape. This is not always the case, since the core may in some instances be made entirely within the one core box. So that the two core parts will properly fit together after they are cured when there are two or more parts to one core, the core depression in the core box is overfilled with the mold sand and then leveled at the top surface of the core box (the strike-off surface) by passing a straight strike-off bar across the core box strike-off surface. The mold sand and bonding agent is abrasive and each time the strike-off bar is passed across the strike-off surface these materials tend to abrade and erode the strike-off surface. In time, it may be seen, that a sufficient amount of the strike-off surface may be removed from the core box by this abrasion that the core depression may become shallower with respect to the strike-off surface. This dimensional error is doubled when the core is formed in two portions, one core box for defining each of the opposite sides of the core. The cores may therefore tend to become smaller and smaller in the dimension corresponding to the depth of the core box so that ultimately the voids in the end cast article (such as a passage through a valve body) become so small that either machining is required to open the passage to acceptable dimensions or new core boxes must be constructed. Either of these two mentioned operations is expensive and time consuming adding to the ultimate cost of the end cast article. Alternatively the end cast articles are provided in a form such that they are dimensionally incorrect.